Supporters of the 2009 Patient Protection and Affordable Care Act (ACA) — so-called Obamacare — have high hopes that when fully implemented, the sweeping reform measure will reduce medical costs and make millions of currently uninsured Americans eligible for health care coverage. But four years after its passage, the law continues to face legal, political and ideological challenges. Conservative Republicans argue that it imposes federal control over medical decisions, and some religiously affiliated employers object to the law’s mandate that preventive-health coverage include contraceptives. Meanwhile, many GOP-led states, especially in the South, are balking at expanding coverage for poor and disabled people under Medicaid, as is urged — but not required — under the law. And some small businesses say expanding health coverage to their workers would be too costly.

Dr. Martha Perez examines Maria Lebron at the Doris Ison Community Health Center, in Miami on Feb. 21, 2013. After initially saying Florida wouldn’t accept federal Medicaid funds, Republican Gov. Rick Scott announced in February that he would support expanding Medicaid in the state. (Getty Images/Joe Raedle)

This is a pivotal year for the controversial 2009 Patient Protection and Affordable Care Act (ACA). The Obama administration — the law’s chief architect — and other supporters hope it will help 30 million more Americans acquire health insurance through two provisions that take effect on Jan. 1, 2014. 1 On that day, millions of uninsured Americans will be newly eligible for Medicaid, which provides medical coverage to low-income and disabled people; and millions of non-Medicaid recipients will be eligible to receive subsidized insurance coverage through government-sponsored insurance markets called exchanges.

The federal Department of Health and Human Services (HHS), state agencies, insurers, hospitals and others are scrambling to meet interim deadlines. Even before coverage expands, however, other programs created under the ACA have been helping to reshape the health care system. Supporters say the changes are holding down costs and increasing doctors’ and hospitals’ focus on keeping patients healthy. But critics say the law is likely having little effect on medical costs, and they accuse the federal government of meddling in the way health care is delivered.